1. Field of the Invention
The present invention relates to a superstructure for an artificial tooth, comprising a root post which is adapted to be screwed into the root canal of a tooth, and a crown anchor.
2. Description of the Prior Art
In a known manner, the general procedure for the construction of artificial teeth, where use can be made of an existing, healthy or repairable root and a stump protruding from the jaw, is shown in FIG. 5. The aforesaid figure represents the state of the art.
In order to produce an artificial tooth, first a tooth anchor inserted in the dentine is required which must form a solid connection with the existing tooth torso; otherwise, the crown will not be solidly connected to the tooth fragment.
FIG. 5 shows a lower jaw molar as an example of the prior art procedure.
Tooth fragment 12 is lodged in jaw bone 10, its upper portion 14 projecting above the upper edge of the jaw bone. Root canal 16 is now cleaned in a manner known per se and enlarged if necessary. In the upper area of tooth stump 12, an essentially cylindrical recess 18 is milled. The two mentioned operations may also be carried out in reverse order. A crown anchor 20 is inserted in the resulting cavity by means of a corresponding tool. The anchor is only roughly schematically shown in FIG. 5, but it is provided with a cylindrical body 22 whose external diameter corresponds to the internal diameter of recess 18 of the tooth and which is centrally and axially provided with a threaded pin 24; the pin 24 being intended to be screwed into the prepared root canal 16.
It may now happen, and it is indeed very often the case, that axis 26 of the prepared root canal, i.e. the axis that is defined as anchor 20 is screwed in, does not coincide with axis 28 of cylindrical recess 18, but rather forms an angle therewith. Since the diameters of recess 18 and of anchor 20 do not differ greatly, the described axial angle results in that the upper edge portion 14 of the tooth stump is broken off as anchor 20 is screwed into tooth 12, until it abuts to the bottom of said recess, as is directly apparent in FIG. 5.